昨天老毕跟我讨论dns的问题，今天想了想，其实实际在生产环境中用到的dns大体有3种：
1.内网调用DNS
一般是每个机房一组，做ms结构，主要功能是供机房内部应用之间调用解析，减少对hosts的依赖，避免硬编码。一般ms结构就可以了，不太会做其他的高可用。
2.回源调用dns
和内网调用dns功能差不多，不过这个是跨机房的调用，而且一般会通过view做智能dns解析。
比较常见的应用场景就是webcdn的回源dns，结构上和内部调用dns差不多。
3.外网dns
提供各种针对外网的解析，A记录，CNAME，MX等等。。
作为用户访问的入口，其重要性也不言而喻，因此对可用性和扩展性以及性能要求会比较高。
一般的做法是在BGP机房做一个高可用的集群做主要的解析工作，同时在双线或者单线机房做一组冷备的高可用DNS集群。
这里讨论下用lvs做dns高可用的方案，主要借鉴了mysql高可用的方案（一般都是一个主库，后面挂多个丛库，丛库前面使用lvs+keepalived做ha，程序写入主库，读取丛库）。
具体的流程如下：
1.用户通过web前端来做dns的增删改等操作（如果是python程序的话，可以通过dnspython操作）。
2.slave通过对比zone文件的serial值来决定是否需要更新记录。
3.用户查询请求至由lvs(dr模式)+keepalived组成的前端负载均衡。
4.lvs分发请求至slave server,最后由slave server直接向用户响应请求。
由于dns一般情况是用udp协议的（关于dns使用的协议可以参考之前的blog），而大家一般都是用lvs做tcp的load balance.
在用lvs实现udp的load balance时主要注意以下几点：
1.添加realserver时选择udp,配置文件中设置
protocol UDP
2.应用的监听IP要设置为vip,在这个场景中可以更改slave dns的设置
listen-on port 53 {vip
;物理ip;};
其中vip用来实现接收lvs的转发包并返回数据给用户，物理ip用来实现master到slave的同步
3.health check需要注意，lvs提供的HTTP_GET和TCP_CHECK都是基于TCP协议的（TCP的SYNC包来检查应用）
对于udp的检查可以使用
MISC_CHECK的方式。
比如下面个设置：
virtual_server vip 53 {
delay_loop 2
lb_algo rr
lb_kind DR
protocol UDP
real_server real_server1 53 {
weight 100
MISC_CHECK {
misc_path "/etc/keepalived/check_named.sh real_server1"
misc_timeout 5
}
}
real_server real_server2 53 {
weight 100
MISC_CHECK {
misc_path "/etc/keepalived/check_named.sh real_server2"
misc_timeout 5
}
}
}
其中/etc/keepalived/check_named.sh的内容如下：
#!/bin/bash
SERVER=$1
OK=`nslookup www.test.com $SERVER|grep ipxxxx`
if [ "$OK" == "" ] ; then
exit 1;
else
exit 0;
fi
即返回0代表dns服务正常，返回1代表服务异常，将会被lvs踢出。
高可用的dns结构图：
最后附一个自己写的spec文件，用来实现chroot的自定义rpm包，继承到yum源中实现dns的快速部署。
Name: Vipshop-Bind-Chroot
Summary: This is for Vipshop dns server.
Group: System Environment/Daemons
Version: 1.0
Release: 0
License: Copyright 2011 Vipshop Inc.
Source: Vipshop-Bind-Chroot-1.0.tar.gz
URL: http://www.vipshop.com
Packager: EricNi
Vendor: Vipshop Inc.
Provides: Vipshop Inc.
BuildRequires: gcc-c++
%description
This is DNS Service pakeage , and it only distributed in Vipshop Servers .
%prep
test -d /usr/local/named && rm -rf /usr/local/named
[ `cat /etc/passwd|grep named|wc -l` -eq 0 ] && useradd named -M -s /sbin/nologin
mkdir -p /usr/local/named /usr/local/named/var/slaves /usr/local/named/var/named /usr/local/named/var/etc /usr/local/named/var/log
mkdir -p /var/named/chroot/etc/namedb /var/named/chroot/etc/log /var/named/chroot/etc/run /var/named/chroot/var/run /var/named/chroot/dev/ /var/named/chroot/etc/namedb/slaves /var/named/chroot/etc/namedb/acl
%setup -n %{name}-%{version}
%build
export BIND_HOME=/usr/local/named
export BIND_CHROOT_HOME=/var/named/chroot
./configure --prefix=${BIND_HOME} --enable-threads --sysconfdir=/etc --disable-openssl-version-check
make
make install
cat > ${BIND_CHROOT_HOME}/etc/named.conf << "EOF"
options {
directory "/etc/namedb";
version "vipshop-cdn-dns";
pid-file "/etc/run/named.pid";
listen-on port 53 {any;};
allow-query {any;};
recursion yes;
dump-file "/etc/namedb/cache_dump.db";
zone-statistics yes;
statistics-file "/etc/namedb/named_stats.txt";
};
logging {
channel warning
{file "/etc/log/named.log" versions 3 size 2048k;
severity warning;
print-severity yes;
print-category yes;
print-time yes;
};
channel query
{file "/etc/log/query.log" versions 3 size 2048k;
severity info;
print-category yes;
print-severity yes;
print-time yes;
};
category queries
{
query;
};
category default
{
warning;
};
};
zone "." IN {
type hint;
file "named.root";
};
zone "localhost" IN {
type master;
file "localhost.zone";
};
zone "0.0.127.in-addr.arpa" IN {
type master;
file "slaves/localhost.rev";
};
zone "vipshop.com" IN {
type master;
file "vipshop.zone";
notify yes;
also-notify {180.186.22.62;};
allow-transfer {
180.186.22.62;
};
};
key "rndc-key" {
algorithm hmac-md5;
secret "f8Na2kl/4NuCNPEZ0f2C1Q==";
};
controls {
inet 127.0.0.1 port 953
allow { 127.0.0.1; } keys { "rndc-key"; };
};
EOF
cat > ${BIND_CHROOT_HOME}/etc/rndc.conf << "EOF"
key "rndc-key" {
algorithm hmac-md5;
secret "f8Na2kl/4NuCNPEZ0f2C1Q==";
};
options {
default-key "rndc-key";
default-server 127.0.0.1;
default-port 953;
};
EOF
cat > ${BIND_CHROOT_HOME}/etc/rndc.key << "EOF"
key "rndc-key" {
algorithm hmac-md5;
secret "f8Na2kl/4NuCNPEZ0f2C1Q==";
};
EOF
cat > /etc/rndc.conf << "EOF"
key "rndc-key" {
algorithm hmac-md5;
secret "f8Na2kl/4NuCNPEZ0f2C1Q==";
};
options {
default-key "rndc-key";
default-server 127.0.0.1;
default-port 953;
};
EOF
cat > ${BIND_CHROOT_HOME}/etc/namedb/named.root << "EOF"
; This file holds the information on root name servers needed to
; initialize cache of Internet domain name servers
; (e.g. reference this file in the "cache . "
; configuration file of BIND domain name servers).
;
; This file is made available by InterNIC
; under anonymous FTP as
; file /domain/named.cache
; on server FTP.INTERNIC.NET
; -OR- RS.INTERNIC.NET
;
; last update: Jan 3, 2013
; related version of root zone: 2013010300
;
; formerly NS.INTERNIC.NET
;
. 3600000 IN NS A.ROOT-SERVERS.NET.
A.ROOT-SERVERS.NET. 3600000 A 198.41.0.4
A.ROOT-SERVERS.NET. 3600000 AAAA 2001:503:BA3E::2:30
;
; FORMERLY NS1.ISI.EDU
;
. 3600000 NS B.ROOT-SERVERS.NET.
B.ROOT-SERVERS.NET. 3600000 A 192.228.79.201
;
; FORMERLY C.PSI.NET
;
. 3600000 NS C.ROOT-SERVERS.NET.
C.ROOT-SERVERS.NET. 3600000 A 192.33.4.12
;
; FORMERLY TERP.UMD.EDU
;
. 3600000 NS D.ROOT-SERVERS.NET.
D.ROOT-SERVERS.NET. 3600000 A 199.7.91.13
D.ROOT-SERVERS.NET. 3600000 AAAA 2001:500:2D::D
;
; FORMERLY NS.NASA.GOV
;
. 3600000 NS E.ROOT-SERVERS.NET.
E.ROOT-SERVERS.NET. 3600000 A 192.203.230.10
;
; FORMERLY NS.ISC.ORG
;
. 3600000 NS F.ROOT-SERVERS.NET.
F.ROOT-SERVERS.NET. 3600000 A 192.5.5.241
F.ROOT-SERVERS.NET. 3600000 AAAA 2001:500:2F::F
;
; FORMERLY NS.NIC.DDN.MIL
;
. 3600000 NS G.ROOT-SERVERS.NET.
G.ROOT-SERVERS.NET. 3600000 A 192.112.36.4
;
; FORMERLY AOS.ARL.ARMY.MIL
;
. 3600000 NS H.ROOT-SERVERS.NET.
H.ROOT-SERVERS.NET. 3600000 A 128.63.2.53
H.ROOT-SERVERS.NET. 3600000 AAAA 2001:500:1::803F:235
;
; FORMERLY NIC.NORDU.NET
;
. 3600000 NS I.ROOT-SERVERS.NET.
I.ROOT-SERVERS.NET. 3600000 A 192.36.148.17
I.ROOT-SERVERS.NET. 3600000 AAAA 2001:7FE::53
;
; OPERATED BY VERISIGN, INC.
;
. 3600000 NS J.ROOT-SERVERS.NET.
J.ROOT-SERVERS.NET. 3600000 A 192.58.128.30
J.ROOT-SERVERS.NET. 3600000 AAAA 2001:503:C27::2:30
;
; OPERATED BY RIPE NCC
;
. 3600000 NS K.ROOT-SERVERS.NET.
K.ROOT-SERVERS.NET. 3600000 A 193.0.14.129
K.ROOT-SERVERS.NET. 3600000 AAAA 2001:7FD::1
;
; OPERATED BY ICANN
;
. 3600000 NS L.ROOT-SERVERS.NET.
L.ROOT-SERVERS.NET. 3600000 A 199.7.83.42
L.ROOT-SERVERS.NET. 3600000 AAAA 2001:500:3::42
;
; OPERATED BY WIDE
;
. 3600000 NS M.ROOT-SERVERS.NET.
M.ROOT-SERVERS.NET. 3600000 A 202.12.27.33
M.ROOT-SERVERS.NET. 3600000 AAAA 2001:DC3::35
; End of File
EOF
cat > ${BIND_CHROOT_HOME}/etc/namedb/localhost.zone << "EOF"
$TTL 86400
$ORIGIN localhost.
@ 1D IN SOA @ root (
42 ; serial (d. adams)
3H ; refresh
15M ; retry
1W ; expiry
1D ) ; minimum
1D IN NS @
1D IN A 127.0.0.1
EOF
cat > ${BIND_CHROOT_HOME}/etc/namedb/localhost.rev << "EOF"
$TTL 86400
@ IN SOA localhost. root.localhost. (
1997022700 ; Serial
28800 ; Refresh
14400 ; Retry
3600000 ; Expire
86400 ) ; Minimum
IN NS localhost.
1 IN PTR localhost.
EOF
cat > ${BIND_CHROOT_HOME}/etc/namedb/vipshop.zone << "EOF"
$TTL 86400
@ IN SOA ns1.vipshop.com. root.vipshop.com. (
2013051501 ; Serial
28800 ; Refresh
14400 ; Retry
3500000 ; Expire
86400 ) ; Minimum
@ IN NS dns1
@ IN NS dns2
localhost IN A 127.0.0.1
img1 IN A xxxx
img3 IN A xxxx
img2 IN A xxxx
img2 IN A xxxx
dns1 IN A xxxx
dns2 IN A xxxx
EOF
cat > /etc/init.d/named << "EOF"
#!/bin/bash
#
# named This shell script takes care of starting and stopping
# named (BIND DNS server).
#
# chkconfig: - 13 87
# description: named (BIND) is a Domain Name Server (DNS) \
# that is used to resolve host names to IP addresses.
# probe: true
# Source function library.
. /etc/rc.d/init.d/functions
# Source networking configuration.
[ -r /etc/sysconfig/network ] && . /etc/sysconfig/network
[ -r /etc/sysconfig/named ] && . /etc/sysconfig/named
[ -f /usr/local/named/sbin/named ] || exit 0
# [ -f /chroot/named/etc/named.conf ] || exit 0
case "$1" in
start)
# Start daemons.
echo -n "Starting named:"
daemon /usr/local/named/sbin/named -c /etc/named.conf -u named -t /var/named/chroot
echo
touch /var/lock/subsys/named
;;
stop)
# Stop daemons.
echo -n "Shutting down named:"
#killproc named
killall named
rm -f /var/lock/subsys/named
echo
;;
status)
#status named
pid=`pidof -o %PPID -x named`
if [ -z $pid ]
then
echo "named is stopped!!!"
else
echo "named is running: pid is $pid"
fi
exit $?
;;
restart)
$0 stop
$0 start
exit $?
;;
reload)
/usr/local/named/sbin/rndc reload
exit $?
;;
probe)
/usr/local/named/sbin/rndc reload >/dev/null 2>&1 || echo start
exit 0
;;
*)
echo "Usage: named {start|stop|status|restart|reload}"
exit 1
esac
exit 0
EOF
chmod 755 /etc/init.d/named
mkdir -p /usr/local/named /usr/local/named/var/slaves /usr/local/named/var/named /usr/local/named/var/etc /usr/local/named/var/log
mkdir -p /var/named/chroot/usr /var/named/chroot/etc/namedb /var/named/chroot/var/run /var/named/chroot/dev/ /var/named/chroot/etc/namedb/slaves /var/named/chroot/etc/run /var/named/chroot/etc/log /var/named/chroot/etc/namedb/acl
chown named:named /var/named/chroot -R
chown 700 /var/named/chroot
mknod /var/named/chroot/dev/null c 1 3
mknod /var/named/chroot/dev/random c 1 8
cp /etc/localtime /var/named/chroot/etc/
sed -i 's/SYSLOGD_OPTIONS=\(.*\)/SYSLOGD_OPTIONS=\"-m 0 -a \/var\/named\/chroot\/dev\/log\"/g' /etc/sysconfig/syslog
/etc/init.d/syslog restart
%pre
if [ ! `grep named /etc/passwd` ];then
useradd -M named -s /sbin/nologin
fi
%post
chkconfig --add named
chkconfig named on
chown named:named /var/named/chroot -R
chown named:named /usr/local/named -R
chown 700 /var/named/chroot
%clean
rm -rf /usr/local/named
rm -rf /var/named
%files
/etc/init.d/named
/usr/local/named/
/var/named/chroot/
%doc
%changelog
* Thu May 16 2013 Ericni .
- Create SPEC file.